Bushes are widely used to support shafts, rods, etc. so that they may (at least) pivot axially relative to the bush and/or bush housing. Sometimes, they may allow complete rotation of the rod or shaft relative to the housing; however, unlike bearings this is not their principle function. Often, it is desirable for bushes to limit or prevent axial movement of the supported rod or shaft; alternatively, sometimes it may be desirable to allow such movement. Bushes used on automobile vehicles are often made of rubber or a similar resilient material and are generally housed in a metal enclosure, for example “U-shaped” housings that can be bolted to the vehicle chassis. Such bushes with housing members are widely used to support automobile “anti-roll bar” assemblies and also general suspension components; typically the housings are bolted to a part of the vehicle chassis or sub-frame. While such bushes provide adequate support and allow at least some rotation (as required) or pivoting of the rod or shaft relative to the bush and housing, they typically have a relatively short life and so require replacement with consequent servicing costs.
Impact resistance of a bush and housing is typically an important characteristic; allowing impact forces to be absorbed rather than resulting in stress-cracking and failure typical of bushes that use rigid components. While the durability of a bush may be increased by using less resilient (springy) construction materials, this tends to result in a bush that has reduced impact resistance. Unfortunately, it is this very desirable quality of resilience (springiness) that leads to the use of rubber or rubber-like materials with their inherent lack of durability.